Semiconductor devices such as LSI and IC generally have external terminals through which semiconductor elements inside the semiconductor devices are electrically connected to external circuits. As an external terminal, an outer lead of a tape carrier is sometimes utilized and a lead of a lead frame or other means is also utilized. The outer lead is connected to an inner lead of the tape carrier, and the inner lead is electrically connected to an internal circuit of a semiconductor device through an electrode pad provided to the surface of the semiconductor device. The lead of the lead frame is electrically connected to the electrode pad via a bonding wire.
The electrode pads are left exposed for a long time before finally being sealed and protected by resin. However, since materials of the electrode pads consist mainly of aluminum or aluminum alloy, their moisture-resistance characteristic is insufficient and they are therefore easily corroded. Consequently, an insulating protective film is provided on the surface of the electrode pad. Since the electrode pads have to be connected to an external circuit connecting means, the insulating protective film is partially removed on the electrode pads to expose the pads and the external circuit connecting means is then connected. The insulating protective film is removed by a so-called excessive removal method in which an insulating protective film of larger area than that of the electrode pad is removed, has usually been used because of the ease of the process. However, by this method, the function of protection will almost be lost because the electrode pad is excessively exposed. Therefore, a so-called partial removal method in which the insulating protective film is partially removed to expose the necessary area of the electrode pad has come to be used. According to this method, since the electrode pad is sufficiently protected, the characteristics of semiconductor devices are not deteriorated.
With reference to FIGS. 14 to 17, a conventional semiconductor device using the partial removal method will be described hereinbelow.
As shown in FIG. 7 which is a plan view of a semiconductor device of the present invention, a semiconductor device 1 having a bump structure is provided with a semiconductor element 10 and a plurality of electrode pads 2 arranged around the outer periphery of the semiconductor element 10, with the semiconductor element 10 and the electrode pads being connected by signal lines 5. FIG. 14 shows a cross sectional view of the electrode pad part of the conventional semiconductor device. The electrode pads 2 are connected to inner leads 15 of a tape carrier by an ILB (Inner Lead Bonding) process, for instance, so that signals can be transmitted or received or a power voltage can be supplied between the electrode pads 2 and the inner lead 15. The ILB is a bonding to connect the electrode pad and the inner lead by a bump.
Next, with reference to FIGS. 14 and 15, the structure of an electrode pad of a conventional semiconductor device will be described. FIG. 15 is a perspective plan view of the structure shown in FIG. 14, with the inner lead 15 omitted. An electrode pad 2 is formed on a semiconductor substrate 11 via an insulating film 12, and the electrode pad 2 is covered with a protective film 9. This protective film 9 is formed with an opening 6 for bump connection, and a bump 7 is formed on the electrode pad via the opening 6 for the bump connection. This bump 7 serves to connect the inner lead 15 to the electrode pad 2. A barrier metal layer 8 is formed between the electrode pad 2 and the bump 7.
Though an example in which a bump is provided on an electrode and the bump is connected to the inner lead of a tape carrier has been described, there is also a wire bonding method in which a fine wire of aluminum or gold is connected to the electrode pad. The other end of the fine wire or the bonding wire is connected to the lead frame and a terminal formed on the lead frame becomes an external terminal of the semiconductor device.
When the inner lead 15 of a tape carrier is heated and pressed by an ILB tool, the force applied to the inner lead is transmitted to the bump 7. This force applied from the inner lead 15 to the bump 7 is transmitted to the electrode pad 2 via the barrier metal layer. The force transmitted to the electrode pad 2 will be transmitted in all directions. However, the transmission of force is hindered at the side and upper surface of the electrode pad 2 resulting the force to concentrate in the downward direction. As a result, the force is transmitted to the semiconductor substrate 11 through the insulating film 12 as a base film. In this case, when the gap between the two adjacent electrode pads is narrow as shown in FIG. 16, the force applied to the electrode pad 2 increases so that a crack 4 occurs in the insulating film 12 under the electrode pad 2 or another crack 3 occurs under between the two adjacent electrode pads 2. As described, the operation of the force at the bonding is explained in the cross sectional views of FIG. 16 and 17.
In the case of the occurrence of cracks 3 or 4 in the insulating film 12, since moisture enters the cracks, the pads are corroded, thus raising a problem in that signals sometimes cannot be transmitted between the electrode pads 2 and the inner leads 15. Furthermore, electric leakage sometimes occurs between the two adjacent electrode pads due to moisture which has entered the crack. The force from the bonding wire which is connected to the lead frame is another force transmitted from the electrode pad to the substrate through an insulating film other than the force transmitted from the inner lead to the bump at ILB. The wire bonding method has the electrode pads on the semiconductor substrate connected to external circuit connection terminals by bonding wires using bonding tools such as capillaries or wedges. Since this bonding is performed by pressing metals to be connected with the application of heat and/or ultrasonic waves, there is a force which is transmitted to the insulating film.
Thus, if the partially removal method described with reference to drawings is employed as the method to expose the electrode pad from the insulating film in place of the excessive removal method, there still exists the problem of damage by the occurrence of cracks in the insulating film because of the concentration of forces applied at bonding, to the insulating film.
With these problems in mind, the object of the present invention is to provide a semiconductor device which does not generate cracks in the insulating film during ILB or wire bonding and the method of manufacturing the same semiconductor device.